Electro-deposition of high saturation magnetization Fe-Ni-Co films

ABSTRACT

High density magnetic recording requires the write head materials to have high saturation magnetic flux density. Preparation of such materials has been achieved by providing an aqueous solution of nickel, iron, and cobalt salts, each present within a specified concentration range, together with selected additives. When used, under the specified operating conditions, as the electrolyte during electro-deposition, said solution provides a ferromagnetic layer having improved magnetic properties, particularly high saturation magnetic flux density. One embodiment of the process teaches formation of pole tips for use in a magnetic write head.

FIELD OF THE INVENTION

[0001] The invention relates to the general field of magnetic films with particular reference to the formation of pole pieces for magnetic recording heads.

BACKGROUND OF THE INVENTION

[0002] High density magnetic recording (>80 Gb/in²) requires thin film inductive write head materials to have high saturation magnetic flux density. FIG. 1 shows a cross-sectional view of a write head. The magnetic field that will write data onto a surface that is a magnetic medium, such as the hard disk in a hard drive, as it moves past the head is generated by electric current in coil 14. Surrounding this coil is upper magnetic layer 13 which is magnetically and physically connected to lower magnetic layer 111 through section 12. The inside of the structure is filled with insulating material 18, such as aluminum oxide. Upper and lower magnetic pole tips, 17 and 15 respectively, complete the magnetic circuit with a narrow non-magnetic gap 16 where the magnetic fringe field will be generated by electric current in coil 14 and is sufficient to write the data.

[0003] In order to generate the high magnetic field near gap 16, all parts of the magnetic circuit in FIG. 1 must be made of soft magnetic materials that have sufficient high saturation magnetic moment, particularly pole tips 15 and 17 through which as much magnetic flux as possible must be ‘squeezed’. Most commonly, such pole tips are electroformed so it is important to develop electro-deposition processes capable of laying down films that have the desired magnetic and mechanical properties.

[0004] Recently, Osaka e al. have described, in U.S. Pat. No. 6,120,918, electro-deposited CoNiFe films consisting of 40-70 wt. % Co, 20-40 wt. % Fe, 10-20 Wt % Ni, and <0.1 wt. % S, having a Bs (saturation magnetic flux induction) of 2.0 T and report having fabricated these CoNiFe films into magnetic recording heads as top and bottom write poles.

[0005] The present invention describes the electro-deposition of similar films having a somewhat different composition which results in improved film properties, both magnetic and physical.

[0006] A routine search of the prior art was performed with the following references of interest being found:

[0007] In U.S. Pat. No. 5,935,403, Suzuki shows a plating method for a FeNiCo layer. Shukovsky et al. in U.S. Pat. No. 5,830,587 and in U.S. Pat. No. 5,571,573, show other plating methods for NiCoFe as well as other layers. U.S. Pat. No. 6,150,046 (Watanabe et al.), U.S. Pat. No. 4,661,216 (Anderson et al.), JP 101997267 (Tachibana Hiroaki), U.S. Pat. No. 6,063,512 (Osaka et al.), and JP11074122 (Ohashi) all are related patents. The above cited prior art does not show the saturation magnetic moment, BS, of the plated film to be greater than 2.0 T. High Bs of the film used for the write-head element is necessary for high density recording technology.

SUMMARY OF THE INVENTION

[0008] It has been an object of at least one embodiment of the present invention to provide a process for the formation, through electro-deposition, of films having high saturation magnetic moment.

[0009] Another object of at least one embodiment of the present invention has been that said process be suitable for forming alloys of nickel, iron, and cobalt.

[0010] Still another object of at least one embodiment of the present invention has been to provide an apparatus for implementing said process.

[0011] A further object of at least one embodiment of the present invention has been to provide a process for forming a magnetic pole piece suitable for use in a magnetic disk write head.

[0012] These objects have been achieved by providing an aqueous solution of nickel, iron, and cobalt salts, each present within a specified concentration range, together with selected additives. When used, under the specified operating conditions, as the electrolyte during electro-deposition, said solution provides a ferromagnetic layer having improved magnetic properties, particularly high saturation magnetic moment. One embodiment of the process teaches formation of a pole piece for use in a magnetic write head.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows a typical write head for a magnetic disk system

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention uses conventional electroplating technology. However, if the particular solution compositions and plating conditions that are disclosed herein are utilized, films having improved properties, both magnetic and physical, realtive to the known prior art, will be obtained.

[0015] In order to obtain, through electroplating, films having a composition between about 50 and 85 weight % iron, between about 0 and 30 weight % nickel, and between about 0 and 50 weight % cobalt, the following aqueous solution was used:

[0016] NiSO₄.6H₂O at a concentration of between 0 and 80 g/L,

[0017] NiCl₂.6H₂O at a concentration of between 0 and 50 g/L,

[0018] CoSO₄.7H₂O at a concentration of between 0 and 50 g/L,

[0019] FeSO₄.7H₂O at a concentration of between 10 and 70 g/L,

[0020] H₃BO₃ at a concentration of between 26 and 27 g/L,

[0021] NH₄Cl at a concentration of between 0 and 20 g/L,

[0022] (NH₄)₂SO₄ at a concentration of between 0 and 20 g/L,

[0023] Sodium Saccharin at a concentration of between 0 and 2.0 g/L, and

[0024] Sodium Lauryl Sulfate at a concentration of between 0.01 and 0.15 g/L.

[0025] Our preferred pH for the process has been about 3.1 but any pH in the range of from 2 to 4 could have been used. pH for the solution was adjusted through controlled addition of H₂SO₄ and NH₃.H₂O. Solution temperature was maintained at between about 10 and 40° C. while films were being deposited, with about 20° C. being preferred. A silicon wafer is used as a substrate for full film electro-deposition. A thin copper seed layer (500-1,000 Å) is sputtered onto the wafer before electro-deposition and made the cathode during electro-deposition.

[0026] Our preferred current density during electro-deposition, was about 15 mA/cm² but the process could still be operated successfully over a current density range of from about 3 to about 30 mA/cm². Anodes of either cobalt or nickel anode could be used.

[0027] As indicated in FIG. 1, a thin film write head has a multilayer structure. Thousands of heads are fabricated on a ceramic Al₂O₃-TiC wafer. In order to electro-deposit pole tips (15 and 17 in FIG. 1) made of the disclosed film, it is necessary to first sputter a metal seed layer (500-1,000 Å) having the same composition as the film to be plated onto the wafer. The conductive seed layer will serve as a cathode during electro-deposition. Then a 3-7 micron thick layer of photoresist is spin coated onto the top of the seed layer, followed by photolithography to create a pattern having the desired pole tip shape within the photoresist layer.

[0028] After a film of the desired composition had been electro-deposited through the resist pattern (typically to a thickness between about 1 and 5 microns), according to the conditions related above, both photoresist and seed layers were removed, resulting in the formation of the pole tip. This was followed by a heat treatment at a temperature between about 100 and 300° C. for between about 60 and 120 minutes in nitrogen, for NiFe and FeCoNi films. CoFe films may craze if treated at high temperature.

[0029] If the above outlined procedures are followed, films having excellent magnetic and physical properties can be obtained. Typically the saturation magnetic moment of the films was between about 2 and 2.2 T. They had coercive fields between about 3 and 17 Oe and anisotropy fields between about 5 and 38 Oe.

[0030] The films had a BCC (body centered cubic) crystal structure and were found to have low internal tensile stress, normally between about 100 and 300 Mpa. A low level of internal stress can prevent the plated film from peeling off the substrate.

[0031] RESULTS:

[0032] In TABLE I below we compare the properties of three films of different composition, deposited according to the teachings of the present invention: TABLE I PROPERTY Fe₈₂Ni₁₈ Fe₆₈Ni₂₁Co₁₁ Fe₆₆Co₃₄ Saturation magnetic 2.1 T 2.2 T 2.2 T flux density Coercive field 3.5 Oe 5.5 Oe 16 Oe Anisotropy field 5.1 Oe 8.9 Oe 34 Oe Electrical resistivity 23 μΩ-cm 23 μΩ-cm — Tensile stress 150 MPa 130 MPa ˜200 MPa

[0033] The significance of the data shown in TABLE I is that the saturation magnetc moment B_(s) is greater than 2 T for the plated film and the films are magnetically soft enough to be used in a write element, such as the pole pieces seen in FIG. 1. 

What is claimed is:
 1. A process for depositing a ferromagnetic film, comprising: forming an aqueous solution that further comprises: NiSO₄.6H₂O at a concentration of between 0 and 80 g/L, NiCl₂.6H₂O at a concentration of between 0 and 50 g/L, CoSO₄.7H₂O at a concentration of between 0 and 50 g/L, FeSO₄.7H₂O at a concentration of between 10 and 70 g/L, H₃BO₃ at a concentration of between 26 and 27 g/L, NH₄Cl at a concentration of between 0 and 20 g/L, (NH₄)₂SO₄ at a concentration of between 0 and 20 g/L, Sodium Saccharin at a concentration of between 0 and 2.0 g/L, and Sodium Lauryl Sulfate at a concentration of between 0.01 and 0.15 g/L. through electro-deposition from said solution, depositing said ferromagnetic film.
 2. The process described in claim 1 wherein said aqueous solution is adjusted to and maintained at a pH between about 2 and
 4. 3. The process described in claim 1 wherein, during electro-deposition, said solution is maintained at a temperature between about 10 and 40° C.
 4. The process described in claim 1 wherein a cobalt anode is used for CoFe plating.
 5. The process described in claim 1 wherein a nickel anode is used for NiFe or FeCoNi plating.
 6. The process described in claim 1 wherein said ferromagnetic film contains between about 50 and 85 weight % iron, between about 0 and 30 weight % nickel, and between about 0 and 50 weight % cobalt.
 7. The process described in claim 1 wherein, during electro-deposition, a current density of between about 3 and 30 mA/cm² is maintained.
 8. A process for manufacturing a pole tip for a magnetic recording head, comprising: on a wafer, forming a conductive seed layer forming a removable photoresist pattern on said conductive seed layer; providing an aqueous solution that further comprises: NiSO₄.6H₂O at a concentration of between 0 and 80 g/L, NiCl₂.6H₂O at a concentration of between 0 and 50 g/L, CoSO₄.7H₂O at a concentration of between 0 and 50 g/L, FeSO₄.7H₂O at a concentration of between 10 and 70 g/L, H₃BO₃ at a concentration of between 26 and 27 g/L, NH₄Cl at a concentration of between 0 and 20 g/L, (NH₄)₂SO₄ at a concentration of between 0 and 20 g/L, Sodium Saccharin at a concentration of between 0 and 2.0 g/L, and Sodium Lauryl Sulfate at a concentration of between 0.01 and 0.15 g/L. adjusting said aqueous solution to have a pH between about 2 and 4; immersing said photoresist pattern in said solution and, using said seed layer as a cathode, electro-depositing material from said solution to a desired thickness inside the pattern; removing said photoresist and said seed layer, thereby forming said pole tip; and then subjecting said pole tip to a heat treatment.
 9. The process described in claim 8 wherein said pole piece is electro-deposited to a thickness between about 1 and 5 microns.
 10. The process described in claim 8 wherein said pole tip is formed by electroplating through a photoresist pattern made using a photolithography process.
 11. The process described in claim 8 wherein a cobalt anode is used for CoFe plating.
 12. The process described in claim 8 wherein a nickel anode is used for NiFe or FeCoNi plating.
 13. The process described in claim 8 wherein said pole piece contains between about 50 and 85 weight % iron, between about 0 and 30 weight % nickel, and between about 0 and 50 weight % cobalt.
 14. The process described in claim 8 wherein said heat treatment further comprises heating NiFe or FeCoNi films at a temperature between about 100 and 300° C. for between about 60 and 120 minutes in nitrogen.
 15. An apparatus for electro-depositing a ferromagnetic film, comprising: an aqueous solution that further comprises: NiSO₄.6H₂O at a concentration of between 0 and 80 g/L, NiCl₂.6H₂O at a concentration of between 0 and 50 g/L, CoSO₄.7H₂O at a concentration of between 0 and 50 g/L, FeSO₄.7H₂O at a concentration of between 10 and 70 g/L, H₃BO₃ at a concentration of between 26 and 27 g/L, NH₄Cl at a concentration of between 0 and 20 g/L, (NH₄)₂SO₄ at a concentration of between 0 and 20 g/L, Sodium Saccharin at a concentration of between 0 and 2.0 g/L, and Sodium Lauryl Sulfate at a concentration of between 0.01 and 0.15 g/L. said aqueous having a pH between 2 and 4; immersed in said solution, a seed layer on which to grow said ferromagnetic film; and means for passing a direct current between the seed layer and an anode.
 16. The apparatus described in claim 15 further comprising means for maintaining said solution at a temperature between about 10 and 40° C. during electro-deposition.
 17. The apparatus described in claim 15 wherein said anode is cobalt during CoFe plating.
 18. The apparatus described in claim 15 wherein said anode is nickel during FeCoNi plating.
 19. The apparatus described in claim 15 wherein said current has a density of between about 3 and 30 mA/cm². 